rewrite admin.js in coffeescript

app/assets/javascripts/admin.js

-$(document).ready(function(){
-    $('input#user_force_random_password').on('change', function(elem) {
-        var elems = $('#user_password, #user_password_confirmation');
-        
-        if ($(this).attr('checked')) {
-            elems.val('').attr('disabled', true);
-        } else {
-            elems.removeAttr('disabled');
-        }
-    });
-});

app/assets/javascripts/admin.js.coffee

+$ ->
+  $('input#user_force_random_password').on 'change', (elem) ->
+    elems = $('#user_password, #user_password_confirmation')
+
+    if $(@).attr 'checked'
+      elems.val('').attr 'disabled', true
+    else
+      elems.removeAttr 'disabled'